[CH:1]1[N:5]2[C:6]3[CH2:17][C:16]4[CH:15]=[CH:14][CH:13]=[CH:12][C:11]=4[C:7]=3[NH:8][C:9](=O)[C:4]2=[N:3][CH:2]=1.[OH-].[Na+].BrCCBr.O>[Br-].C([N+](CCCC)(CCCC)CCCC)CCC.CS(C)=O.C(O)(=O)C>[CH2:1]1[N:5]2[C:6]3[CH2:17][C:16]4[CH:15]=[CH:14][CH:13]=[CH:12][C:11]=4[C:7]=3[NH:8][CH:9]=[C:4]2[N:3]=[CH:2]1
A suspension of 1.3 g of 5H,10H-imidazo-[1,2-a]indeno[1,2-e]pyrazin-4-one, 2 g of sodium hydroxide pellets and 32 mg of tetrabutylammonium bromide in 10 ml of dry dimethyl sulphoxide is stirred at a temperature in the region of 18° C. A solution of 0.4 ml of 1,2-dibromoethane in 5 ml of dimethyl sulphoxide is then added and the stirring is continued overnight at a temperature in the region of 20° C. The reaction mixture is poured into a mixture of water and ice (250 ml), acidified with 8 ml of acetic acid and kept stirring for 1 hour 30 minutes. The solid formed is then filtered off and it is purified by chromatography on a column of silica (100 g) with a mixture of dichloromethane and methanol (95/5 by volume). After drying at 60° C., 0.45 g of spiro[5H,10H-imidazo[1,2-a]indeno[1,2-e]pyrazine-10:1'-cyclopropane]-4-one is obtained, in the form of a pink solid melting above 260° C. (Analysis % calculated C: 72.28, H: 4.45, N: 16.86, O: 6.42, % found C: 71.8, H: 4.4, N: 16.3).
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